1. Field of the Invention
The present invention relates to global satellite communication systems and more particularly to a global satellite communication system providing transmission protocol conversion for cellular radiotelephone systems based on the geographic coverage areas provided.
2. Description of the Prior Art
Numerous nationwide communication systems, such as nationwide paging systems, have also been proposed and a number of such systems are currently in operation around the world. While these systems fulfill the need to deliver information on a limited nationwide basis, they fall short of providing true nationwide information delivery. This is due to the fact that such nationwide systems were limited only to those service areas where the nationwide system service provider had a communication system infrastructure in place, which was generally only in the major metropolitan areas. Such nationwide systems have provided a centralized message input, or collection, point to which all messages to be handled by the system were directed. The messages were then distributed by landline or by satellite to each of the cities in the network. The messages, as they were received in each of the network cities, were then processed as a conventional message for transmission throughout the local systems. Because the messages were transmitted throughout the nationwide system, problems with message throughput are expected as the number of subscribers belonging to the system increases.
Networking such nationwide systems to provide information delivery on a global basis reaching far beyond the immediate boundaries of the nationwide system service provider is a goal of many of these systems. However, such systems would at best, only provide limited global system coverage in the manner described for the present nationwide systems. It would also be anticipated that the problems with message throughput would become even more severe when the messages are distributed throughout the global system, and transmitted in each of the cities making up the global system.
One solution to the problem of limited nationwide paging coverage, and complete global paging coverage, is by means of a satellite based communication system, in which the satellite, or satellites, would be active in transmitting the messages directly to the ground based communication receivers. The success of such a satellite based communication system would depend directly on how many users can be covered by the system to help defray the very high costs associated with satellite systems, both paging users and cellular radiotelephone users. In addition, the acceptance of a global communication system would depend on the utility the system offers the end-users.
Acceptance of a satellite based communication system is complicated by the fact that there are several "standard" paging protocols, and several "standard" cellular transmission protocols in use around the world. These paging protocols include such digital signaling formats as the Golay Sequential Code (GSC) and POCSAG signaling formats, and such analog tone signaling formats as the Motorola 5/6-tone signaling format and the ZVEI and CCIR 6-tone signaling formats. Many other signaling formats are in use, as well, around the world. New signaling standards, such as the ERMES European paging standard will also be in place in the future. To facilitate a global satellite communication system, the system would have to provide service in a number of signaling formats in order to gain the broad acceptance required to make such a system cost effective.
Numerous cellular communication systems are in use today which operate using well known cellular signalling protocols. New cellular signalling protocols are being proposed to improve cellular communications and the number of subscribers which may be handled within the systems. The conventional and new cellular communication protocols are not compatible. As a result, communication between cellular transceivers operating in one cellular communication system cannot directly communicate to cellular radiotelephones operating in non-compatible cellular communication systems without first converting to an analog voice message which is handled through the public switched telephone network. When cellular radiotelephones become available to communicate directly through satellites, cellular radiotelephones will be unable to communicate directly, again due to the cellular communication protocol differences which can be present. There is a need to provide geographic protocol conversion of cellular communication protocols to enable communication between non-compatible cellular communication systems. To facilitate a global satellite cellular transmission system, the system would have to provide service in a number of cellular transmission protocols also in order to gain the broad acceptance required to make such a system cost effective.
In addition to the problems associated with processing multiple signaling formats and cellular transmission protocols, the assignments of operating frequencies for pagers and cellular radiotelephones operating in the global system is subject to national and regional conventions regulated by the International Telecommunications Union (ITU) and national regulatory agencies, such as the Federal Communications Commission (FCC), as the communication satellite sweeps over the earth. This would require the satellite communication system to adhere to the local laws and regulations in a particular nation or region in order that service be provided on a global basis. Such a satellite based communication system must be capable of selectively transmitting over limited geographic areas on a number of different operating frequencies.
Pagers operating within the system which allow the end-user to roam, or travel, from place-to-place throughout the world would also need to be frequency-agile, in order for the pager to maintain communication with the satellite transmissions throughout the world. However, because the satellites are capable of delivering messages in a variety of signaling formats, the requirement of the pager to process different signaling formats is eliminated.